It's been a long wait, but the GreenPois0n jailbreak by Chronic Dev-Team has finally made its way to the Mac. Available Here: Greenpois0n.com

Here's a Windows install tutorial, but the jailbreak is carried out the same way on the Mac: How To

The quick history behind it was that they had developed Greenpois0n using the SHAtter exploit. They shared that exploit code with Geohot under the understanding that he would not release his jailbreak before they did. He did it anyway, but with his own code. That caused the team to have to scramble to rework the JB to use Geohot's exploit in order to avoid revealing two exploits to Apple, and allowing the company to patch both. Over the past few weeks, the team has been working to get each version out. First it was Windows, then Linux came a few days later and the Mac version is now available.